1. Field of the Invention
This invention relates to an automatic focus detecting apparatus for an optical system.
2. Description of the Prior Art
Various automatic focus detecting apparatuses have heretofore been proposed. For example, Japanese Laid-Open Patent Application No. 15432/1976 discloses a technique in which first and second light rays at two positions spaced apart from the optical axis of an image formation optical system are separated from a light beam immediately after the beam is passed through the image formation optical system. The separated first and second light rays impinge on first and second photosensitive element arrays disposed at predetermined focus positions of the first and second light rays in accordance with the in-focus and out-of-focus conditions of the image formation optical system. The outputs of the individual photosensitive elements of the first array are compared with the outputs of the corresponding photosensitive elements of the second array, and detection of the focus is effected in accordance with the result of the individual comparisons. This technique suffers from a disadvantage in that discrimination is made only as to whether the image formation optical system is in focus or out of focus and cannot be made as to whether the actual focal plane is forward (hereinafter referred to as forward focusing) or rearward (hereinafter referred to as backward focusing) with respect to a predetermined focal plane and as to the degree of the out-of-focus condition.